It has long been recognized that the properties of polymers can be tailored to a high degree through variables such as polymer sequence, structure, additive and filler incorporation, composition, morphology, thermodynamic and kinetic processing control. It is similarly known that various sizes and shapes of fillers, and particulates (e.g. calcium carbonate, silica, carbon black etc.), and resins can also be incorporated into polymers or monomer mixtures to enhance their physical and material properties.
Polymer formulations useful in photoresists are highly engineered systems and thereby utilize nearly all of the prior known techniques for manipulation of properties. Additionally, photoresist polymers require high degrees of purity in order to perform their imaging and etch functions optimally and to ensure electronic circuit reliability. Recent art (WO 2004/040371) has focused on modifications of photoresists through the incorporation of nanostructured chemical entities known as POSS which provide filler type reinforcement but in the form of a soluble chemical entity. Optimal performance of photoresists can only be obtained through use of high purity POSS molecules.
Current engineering practices produce POSS molecules in high yield but they also require further refinement to render them suitable in photoresist applications. Prior methods discussed in U.S. patent application Ser. Nos. 09/631,892 and 10/186,318 (incorporated herein by reference) describe the utility of both protic acids and hydroxide containing bases to promote the silation of POSS silanols with silane coupling agents. While these approaches are known to be generally effective, they are limited in that protic acids and hydroxide bases can also catalyze the self condensation of POSS silanols into oligomerized resins (FIG. 1). Such resins are known as polysilsesquioxanes or T-resins and are not desirable in photoresists as their structure is molecularly imprecise, they contribute to blockiness and morphological irregularity, they increase viscosity, reduce shelf life, and cause difficulties in the filtration of photoresist formulations.
The keys that enable nanostructured chemicals to function as 1-10 nm reinforcing agents are: (1) their unique size with respect to polymer chain dimensions, and (2) their ability to be compatibilized with polymer systems to overcome repulsive forces that promote incompatibility and expulsion of the nanoreinforcing agent by the polymer chains. That is, nanostructured chemicals can be tailored to exhibit preferential affinity/compatibility with some polymer microstructures through variation of the R groups on each nanostructure. At the same time, the nanostructured chemicals can be tailored to be incompatible or compatible with other microstructures within the same polymer, thus allowing for selective reinforcement of specific polymer microstructure. Therefore, the factors to effect a selective nanoreinforcement include specific nanosizes of nanostructured chemicals, distributions of nanosizes, and compatibilities and disparities between the nanostrucutured chemical and the polymer system. For POSS, dispersion of the molecules and their compatibility with polymer segments is thermodynamically governed by the free energy of mixing equation (ΔG=ΔH−TΔS). The nature of the R group and ability of the reactive groups on the POSS cage to react or interact with polymers and surfaces greatly contributes to a favorable enthalpic (ΔH) term while the entropic term (ΔS) for POSS is highly favorable because of the monoscopic cage size and distribution of 1.0.
Nanostructured chemicals are best exemplified by those based on low-cost Polyhedral Oligomeric Silsesquioxanes (POSS) and Polyhedral Oligomeric Silicates (POS). POSS systems contain hybrid (i.e. organic-inorganic) compositions in which the internal cage like framework is primarily comprised of inorganic silicon-oxygen bonds. The exterior of the nanostructure is covered by both reactive and nonreactive organic functionalities (R), which ensure compatibility and tailorability of the nanostructure with organic monomers and polymers. These and other properties and features of nanostructured chemicals are discussed in detail in U.S. Pat. No. 5,412,053 and U.S. Pat. No. 5,484,867 to Lichtenhan et al., which are expressly incorporated herein by reference in their entirety.
Consequently a need exists for improvement upon the prior art methods of POSS silations which result in the formation of nanostructured monomers. An improved process yielding, higher purity, and molecularily precise silated POSS systems is described.